Carburetor

ABSTRACT

In an air valve carburetor the air valve is connected by a link to a slot formed in one end of a lever pivoted at the opposite end. Intermediate the slot and the pivot point, a hanger extends from the lever to a metering rod to position the metering rod in accordance with air valve position. An ambient air pressure and temperature responsive device and a manifold vacuum responsive device are connected in series and position the link in the slot to maintain proper mixture ratio and to select desired mixture ratios. A thermostat responsive to engine operating temperature moves the lever pivot point to provide cold enrichment.

I United States Patent 1191 1111 3,882,206 Gural et al. May 6, 1975 CARBURETOR 3,721,428 3/1973 Gele et al 261/39 B [75] Inventors: John A. Gural, Pittsford, N.Y.;

Stanley H. Mick, Mt. Clemens, 'f 9 Mich; John w Moulds pent-61d, Assistant Exammer-F. R. Bilmsky Attorney, Agent, or FirmC, K. Veenstra [73] Assignee: General Motors Corporation,

Detroit, Mich. {57] ABSTRACT [22] Filed: Mar. 21, 1973 In an air valve carburetor the air valve is connected by a link to a slot formed 1n one end of a lever pivoted at [21] Appl. No.: 343,553 the opposite end. Intermediate the slot and the pivot point, a hanger extends from the lever to a metering [52] Us. Cl 261/39 261/50 M rod to position the metering rod in accordance with [51] Int. h 7/18 air valve position. An ambient air pressure and tem- [58] Field of Search 261/39 X3 B 39 C perature responsive device and a manifold vacuum re- 261/50 A 3 sponsive device are connected in series and position the link in the slot to maintain proper mixture ratio [56] References Cited and to select desired mixture ratios. A thermostat re sponsive to engine operating temperature moves the 2 082 293 :T PATENTS 261/39 B lever pivot point to provide cold enrichment.

Inga 3,284,063 11/1966 Bickhaus et al 261/39 B 8 Claims 8 Drawing Figures 45 36 60 25 #8 ix )0 a 52 5? 5 a2 a? O 53 5a 0 68 as as 86 w a4 22 i w t 28 8*! "I00 .13 s o s w I Z8 Z0? 2oz 90 20 1s WENTEMY 8 I975 SHEU 3 0F 4 1 32 I49 54 126 I52 158 56 5 30 I52 2 TO VACUUM BREAK+ MANIFOLD VACUUM PATENIEDHM' ems 3,882.206

saw u or 4 :61; MANIFOLD 4 VACUU M CARBURETOR This invention relates to an air valve carburetor for internal combustion engines and more particularly to such a carburetor having a novel linkage interconnecting the air valve with the metering rod. The linkage permits incorporation of controls responsive to ambient air temperature and pressure for maintenance of proper mixture ratio, responsive to manifold vacuum for selecting desired mixture ratios, and responsive to engine operating temperatures for cold enrichment.

The carburetor provides a number of advantages over known prior art air valve carburetors, notably providing a versatile metering linkage which may be disposed in a protected region free from both the environment directly within the carburetor fuel bowl and the external environment surrounding the carburetor.

The details as well as other objects and advantages of this invention are set forth in the remainder of the speciftcation and are shown in the drawings in which:

FIG. 1 is a sectional elevational view of the carburetor showing the basic metering linkage;

FIGS. 2 and 3 are enlarged views of the metering rod showing the configuration of the tapered portion;

FIG. 4 is a view of a carburetor similar to FIG. 1 further having controls responsive to ambient air pressure and temperature and to manifold vacuum;

FIG. 5 is a view of a carburetor with metering linkage similar to FIG. 4 further having a lever positioned in response to engine operating temperature; and

FIGS. 6, 7 and 8 are side elevational views of the FIG. 5 carburetor having parts broken away to show the cold enrichment mechanism in cold start, normal start, and hot start positions respectively.

Referring first to FIG. 1, the carburetor 10 has a mix ture conduit 12 including an air inlet 14 and a mixture outlet 16 which discharges to the engine. A throttle 18 is disposed in mixture outlet 16 in the usual manner on a throttle shaft 20.

An air valve 22 is disposed in air inlet 14 on an air valve shaft 24. A spring 26 is hooked over the downstream edge 28 of air valve 22 or otherwise attached thereto and extends to a bracket 30 to bias air valve 22 to the position shown.

A tang 32 reaches upwardly from air valve 22 and is connected by a link 34 to a diaphragm 36. A chamber 38, formed between the right side of diaphragm 36 and a cover member 40, is connected by a tube 42 to a region 44 of mixture conduit 12 defined between air valve 22 and throttle 18.

A chamber 46, defined between the left side of diaphragm 36 and a cover member 48, is subjected to substantially atmospheric pressure, present in air inlet 14 and in the air cleaner (not shown), through openings such as 50, 52 and 54. (The air cleaner seats on a rim 56 disposed about the upper portion of carburetor 10.)

In operation, chamber 38 is subjected to the subat' mospheric pressure created in region 44 as throttle 18 is opened, and diaphragm 36 acts through link 34 to pull air valve 22 clockwise to an open position. Spring 26 is effective to balance the opening force of diaphragm 36, thereby creating a substantially constant subatmospheric pressure in region 44. By thus establishing a generally constant pressure drop across air valve 22, the area about air valve 22 and thus the rotative position of air valve 22 is determined by and is a measure of the rate of air flow through mixture conduit 12.

A tab 58 extends upwardly from air valve 22 and is connected through a link 60 to one end 62 of a lever 64. The opposite end 66 of lever 64 is pivoted about a pin 68. Intermediate ends 62 and 66, a hanger 70 extends from lever 64 into the carburetor fuel bowl 72. The lower end 74 of hanger 70 has a hook 76 which is received in a recess 78 formed in a metering rod 80.

It may be noted that hanger 70 extends through an opening 82 in the cover 84 for fuel bowl 72. Opening 82 is closed by a slider 86 which shifts horizontally during movement of hanger 70.

Metering rod is disposed in a fuel passage 88 having its lower end 90 disposed to receive fuel from a well 92 formed in the bottom of fuel bowl 72. The upper end 94 of fuel passage 88 has an opening 96 through which fuel is discharged into region 44 of mixture conduit 12. It will be appreciated, therefore, that the fuel in fuel bowl 72 is subjected to a substantially constant metering head from the substantially atmospheric pressure in the upper portion of the fuel bowl to the generally constant pressure in region 44.

A metering jet or orifice 98 is disposed in fuel passage 88 around the tip 99 of metering rod 80. As best shown in FIGS. 2 and 3, metering rod 80 has flat tapered surfaces 100 on opposite sides which, upon reciprocation of metering rod 80 in jet 98, varies the area available for fuel flow through jet 98.

In operation, as air valve 22 opens by clockwise rotation, link 60 rotates lever 64 in a clockwise direction. Lever 64 then lifts hanger 70 to move metering rod 80 generally upwardly and rightwardly in fuel passage 88. Thus as air valve 22 is opened to increase the area available for air flow through air inlet 14, metering rod 80 is shifted to increase the area available for fuel flow through metering orifice 98. By this means, a substantially constant air-fuel ratio may be maintained the precise proportion being controlled by the geometry of tapered surfaces 100 and of the linkage between air valve 22 and metering rod 80.

A spring 102 extends from a ledge 104 formed in fuel passage 88 to the lower end 106 of metering rod 80 to take up any slack in the linkage and to load metering rod 80 against jet 98.

It may be noted from FIG. 3 that the thickness of metering rod 80 increases from the end of surfaces 100 most closely adjacent passage inlet 90 to tip 99. Tip 99 is therefore enlarged and assists in discharging fuel from fuel passage 88 as air valve 22 and metering rod 80 are moved to increase air and fuel flow. This offsets the greater inertia of the fuel which otherwise could create a mixture temporarily leaner than desired.

Referring now to FIG. 4, a slot 108 is formed in the end 62 of lever 64'. Link 60 is connected to lever 64' by having one end 110 disposed in slot 108. A link 112 extends from 110 to an arm 114 of a supplementary lever 116 pivoted at 118. The opposite arm 120 oflever 116 is connected by a link 122 to one end 124 of an aneroid 126. The opposite end 128 of aneroid 126 is connected to a reciprocable plunger 130 threadedly received by an adjusting screw, guided in the bore 134 of an adjustable stop 136, and extending to a diaphragm 138.

A chamber defined between the right side of diaphragm 138 and a cover member 142 is subjected to the manifold vacuum in mixture outlet 16 downstream of throttle 18, while a chamber 144 defined between the left side of diaphragm 138 and a cover member 146 is subjected to atmospheric pressure. The resulting rightward bias on diaphragm 138 is resisted by a spring 148 disposed between the head 149 of adjusting nut 132 and a support 150. The linkage is shown in the position assumed when manifold vacuum is sufficient to overcome the force of spring 148.

When throttle 18 is opened and manifold vacuum drops to a point indicative of the need for an enriched air-fuel ratio, spring 148 moves adjusting screw 132 leftwardly until head 149 engages adjustable stop 136. Link 130 is thus moved leftwardly, and a spring 151, extending between end 120 of supplementary lever 116 and a support 152, moves supplementary lever 116 counterclockwise to move link 122 and aneroid 126 leftwardly. Link 112 is then pulled downwardly to reposition end l of link 60 in slot 108, thereby resulting in a shorter lever arm defined between end 110 of link 60 and pivot pin 68. This increases the travel of metering rod 80 through metering jet 98 for equivalent opening movement of air valve 22 to provide an enriched air-fuel mixture.

When manifold vacuum increases to a point indicative of a need for a leaner air-fuel ratio, diaphragm 138 forces link 130 and adjusting screw 132 rightwardly until the end 154 of adjusting screw 132 engages support 150. This forces aneroid 126 and link 122 rightwardly resulting in clockwise rotation of lever 116. Link 112 then raises the end 110 of link 60 in slot 108 to increase the lever arm defined between link end 110 and pivot pin 68. This reduces the travel of metering rod 80 through metering jet 98 for equivalent opening movement of air valve 22 to provide a lean air-fuel mixture.

Upon a decrease in ambient air pressure or an increase in ambient air temperature, both indicative of a reduction in air density and consequently a reduction in the mass rate of air flow through air inlet 14 for equivalent volume air flow, aneroid 126 expands forcing link 122 rightwardly and causing clockwise rotation of lever 116. Link 112 then raises the end 110 of link 60 in slot 108 to increase the lever arm defined between link end 110 and pivot pin 68. The increased lever arm reduces the travel of metering rod 80 in metering jet 98 for equivalent movement of air valve 22 to prevent air'fuel mixture enrichment caused by a reduction in air density.

Upon an increase in ambient air pressure or a decrease in ambient air temperature, both indicative of an increase in air density, aneroid 126 contracts. Spring 151 then causes counterclockwise rotation of supplementary lever 116, and link 112 then moves link end 110 downwardly in slot 108 to shorten the lever arm defined between end 110 and pivot pin 68. The shortened lever arm increases the travel of metering rod 80 in jet 98 for equivalent movement of air valve 22 to prevent leaning of the air-fuel mixture due to an increase in air density.

Referring now to FIGS. 6, 7 and 8, a housing 156 encloses a thermostat 158 subjected to engine operating temperatures for example, by passing air in heat exchange relationship with engine exhaust gases and then through housing 156. Thermostat 158 positions a shaft 160 to which a thermostat lever 162 is secured. A link 164 extends from thermostat lever 162 to an intermediate lever 166 pivotally mounted about a cold enrichment shaft 168.

A vacuum break lever 170 is secured to cold enrichment shaft 168 and has a tang 172 engaged by an arm 174 of lever 166. A link 176 extends from vacuum break lever 170 and is received in a slot 178 formed in the plunger 180 of a vacuum break unit 182.

Vacuum break unit 182 includes a diaphragm 184 biased toward the position shown by a spring 186. A chamber 188, defined between the right side of diaphragm 184 and a cover member 190, is subjected to the manifold vacuum in mixture outlet 16 downstream of throttle 18. A chamber 192, defined between the left side of diaphragm 184 and a cover member 194, is subjected to atmospheric pressure. As soon as the engine starts, or after a suitable time delay provided by known time delay units, diaphragm 184 is pulled rightwardly against the bias of spring 186. A washer 196, secured to diaphragm 184, then pulls a cup member 198 toward the right. This compresses a spring 200 to pull plunger 180 toward the right. Link 176 is thus moved rightwardly to rotate vacuum break lever 170 and cold enrichment shaft 168 in a clockwise direction the degree of rotation being limited by engagement of tang 172 with arm 174 when the force exerted by spring 200 is balanced by the force exerted by thermostat 158. The resulting counterclockwise movement of a cold enrichment lever 202, shown in FIG. 5 and secured to cold enrichment shaft 168, carries pivot pin 68 and thus moves lever 64' to increase the lever arm defined between link end 220 and pivot pin 68. This reduces travel of metering rod in jet 98 for equivalent movement of air valve 22 and thus leans the air-fuel mixture after the engine starts.

As thermostat 158 is thereafter warmed during engine operation, thermostat lever 162 is rotated clock wise as viewed in FIGS. 6-8. Lever 162 then acts through link 164 to rotate intermediate lever 166 clockwise as viewed in FIGS. 6-8. This permits further clockwise rotation of vacuum break lever 170 and cold enrichment shaft 168 under the force imparted by vacuum break unit 182 which thus impart counterclockwise rotation to cold enrichment lever 202 as viewed in FIG. 5. The resulting counterclockwise movement of pivot pin 68 carried by cold enrichment lever 202 on enrichment shaft 168 moves lever 64' with respect to link 60 and thus increases the lever arm defined between link end and pivot pin 68. This increase in lever arm reduces the travel of metering rod 80 in jet 98 for equivalent movement of air valve 22 to lean the air-fuel mixture as the engine warms. This will continue as the engine warms until a tang 204 on vacuum break lever engages an adjustable stop 206 as shown in FIGS. 7 and 8.

As thermostat 158 cools after engine operation, thermostat lever 162 is rotated counterclockwise as viewed in FIGS. 68. Lever 162 then acts through link 164 to rotate intermediate lever 166 counterclockwise as viewed in FIGS. 6-8. At a selected temperature, arm 174 on lever 166 engages tang 172 on vacuum break lever 170 to move lever 170, and cold enrichment shaft 168, counterclockwise away from stop 206 as shown in FIG. 6. This imparts clockwise rotation to cold enrichment lever 202 as viewed in FIG. 5, and the resulting clockwise movement of pivot pin 68 shifts lever 64'. As lever 64' is shifted, metering rod 80 is raised to provide increased fuel flow for cold start. In addition, the lever arm defined between link end 110 and pivot pin 68 is decreased to provide increased travel of metering rod 80 in jet 98 for equivalent movement of air valve 22 and thus provide an enriched air-fuel mixture for cold operation.

Referring again to FIGS. 6-8, a link 208 extends from intermediate lever 166 and is received in a slot 210 of a fast idle cam member 2l2. Fast idle cam member 212 has a series of steps 214 or alternatively a smoothly contoured surfacc engaged by a fast idle adjusting screw 216 carried in a tang 218 of a lever 220 pivoted on throttle shaft 20. Another tang 222 on lever 220 engages an arm 224 of a throttle lever 226 secured to throttle shaft 20. A link 228 extends from throttle lever 226 and is received in a slot 230 of an air valve lever 232 secured to air valve shaft 24. A tang 234 on air valve lever 232 carries an idle mixture adjusting screw 236 which engages an arm 238 on fast idle cam member 212.

In operation, as the temperature decreases thermostat 158 rotates thermostat lever 162 counterclockwise to lift link 164 and rotate intermediate lever 166 counterclockwise. Link 208 is then pulled upwardly and toward the right to rotate fast idle cam member 212 clockwise. Fast idle adjusting screw 216 is then received on the high step 214 of fast idle cam member 212 to limit clockwise movement in the throttle closing direction of lever 220, throttle lever 226 and throttle shaft 20.

As throttle lever 226 is rotated counterclockwise during opening movement of throttle l8, link 228 is pulled downwardly to provide counterclockwise rotation of air valve lever 232 and air valve shaft 24 to assist in opening air valve 22. When needed to unload a flooded engine, throttle 18 can be opened completely. This rotates lever 226 counterclockwise and link 228 then opens air valve 22 partially so that little, if any, vacuum is produced in region 44 and fuel flow is minimized.

As thermostat 158 is warmed during engine operation, thermostat lever 162 and link I64 pull intermediate lever 166 in a clockwise direction, as viewed in FIGS. 6-8. This pushes link 208 downwardly and toward the left to permit counterclockwise movement of fast idle cam member 212. Fast idle adjustment screw 2l6 then may engage a lower step 214 on fast idle cam member 212, permitting further movement of lever 220, throttle lever 226 and throttle shaft in the clockwise or throttle closing direction to reduce engine idle speed.

As shown in FIG. 8, at high temperatures thermostat 158 positions thermostat lever 162, link 164, intermediate lever 166, link 208, and fast idle cam member 212 whereby arm 238 is engaged by idle mixture adjusting screw 236. This limits movement of air valve lever 232 and air valve shaft 24 in the clockwise or air valve closing direction to prevent an overly rich idling air-fuel mixture.

In the foregoing, the term aneroid has been used to describe a bellows responsive to ambient air temperature and/or pressure. When response to atmospheric pressure alone is desired, an evacuated bellows will be used. When response to both atmospheric pressure and temperature is desired, a gas filled bellows will be used.

It will be appreciated that link 60 and lever 64' are, and other components may be, contoured to provide different lever arms in different linkage positions. This permits tailoring of the metering rod response to air valve movement for increased control over the air-fuel ratios provided at various rates of air flow. In some circumstances, for example, the linkage may be con toured to provide first a decrease and then an increase in the lever arm defined between link end and pivot pin 68 as air valve 24 opens.

it will be noted from the foregoing that all of the metering linkage is disposed in a protected area free from the potentially troublesome environments both exterior of the carburetor and directly with the carburetor fuel bowl 72. The metering linkage is separated by the fuel bowl cover from contact with liquid fuel and the concommitant potential for deposits on linkage connections, and the linkage is protected from dirt and damage exterior to the carburetor by its location within the air cleaner rim 56. All of this is made possible by the configuration of the metering linkage set forth herein.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. A carburetor comprising a mixture conduit having an air inlet and a mixture outlet, a throttle disposed in said mixture outlet and controlling flow therethrough, an air valve rotatably disposed in said air inlet, means controlling said air valve whereby its rotative position is a measure of the rate of air flow through said air inlet, a fuel bowl, a fuel passage receiving fuel from said fuel bowl and discharging fuel into said mixture conduit, a metering orifice disposed in said fuel passage, a metering rod associated with said metering orifice and controlling the area thereof to control the rate of fuel flow from said fuel bowl through said passage and said orifice to said mixture conduit, a pivot pin, a lever pivoted on said pin, said lever having a first lever arm connected to said metering rod and a second lever arm, a link connected to said air valve and to said second lever arm whereby the positions of said lever and said metering rod are controlled by the rotative position of said air valve and the rate of fuel flow through said passage to said mixture conduit is proportioned to the rate of air flow through said air inlet, said second lever arm having a slot formed therein and receiving said link, and operating condition responsive means controlling the position of said link in said slot whereby the length of said second lever arm may be varied to adjust the proportion of fuel flow to air flow, said operating con dition responsive means including an aneroid responsive to inlet air pressure and operative to increase the length of said second lever arm upon a decrease in inlet air pressure whereby a proper proportion of fuel flow to air flow is maintained upon a decrease in inlet air pressure.

2. A carburetor comprising a mixture conduit having an air inlet and a mixture outlet, a throttle disposed in said mixture outlet and controlling fiow therethrough, an air valve rotatably disposed in said air inlet, means controlling said air valve whereby its rotative position is a measure of the rate of air flow through said air inlet, a fuel bowl, a fuel passage receiving fuel from said fuel bowl and discharging fuel into said mixture conduit, a metering orifice disposed in said fuel passage, a metering rod associated with said metering orifice and controlling the area thereof to control the rate of fuel flow from said fuel bowl through said passage and said orifice to said mixture conduit, a pivot pin, a lever pivoted on said pin, said lever having a first lever arm connected to said metering rod and a second lever arm, a link connected to said air valve and to said second lever arm whereby the positions of said lever and said metering rod are controlled by the rotative position of said air valve and the rate of fuel flow through said passage to said mixture conduit is proportioned to the rate of air flow through said air inlet, said second lever arm having a slot formed therein and receiving said link, and operating condition responsive means controlling the position of said link in said slot whereby the length of said second lever arm may be varied to adjust the proportion of fuel flow to air flow, said operating condition responsive means including a device responsive to inlet air temperature and operative to increase the length of said second lever arm upon an increase in inlet air temperature whereby a proper proportion of fuel flow to air flow is maintained upon an increase in inlet air temperature.

3. A carburetor comprising a mixture conduit having an air inlet and a mixture outlet, a throttle disposed in said mixture outlet and controlling flow therethrough, an air valve rotatably disposed in said air inlet, means controlling said air valve whereby its rotative position is a measure of the rate of air flow through said air inlet, a fuel bowl, a fuel passage receiving fuel from said fuel bowl and discharging fuel into said mixture conduit, a metering orifice disposed in said fuel passage, a metering rod associated with said metering orifice and controlling the area thereof to control the rate of fuel flow from said fuel bowl through said passage and said orifice to said mixture conduit, a pivot pin, a lever pivoted on said pin, said lever having a first lever arm con nected to said metering rod and a second lever arm, a link connected to said air valve and to said second lever arm whereby the positions of said lever and said metering rod are controlled by the rotative position of said air valve and the rate of fuel flow through said passage to said mixture conduit is proportioned to the rate of air flow through said air inlet, said second lever arm having a slot formed therein and receiving said link, and operating condition responsive means controlling the position of said link in said slot whereby the length of said second lever arm may be varied to adjust the proportion of fuel flow to air flow, said operating condition responsive means including a device responsive to pressure in said mixture conduit downstream of said throttle and operative to decrease the length of said second lever arm upon an increase in such pressure above a selected level whereby the proportion of fuel flow to air flow is increased upon an increase in such pressure above such level.

4. A carburetor comprising a mixture conduit having an air inlet and a mixture outlet, a throttle disposed in said mixture outlet and controlling flow therethrough, an air valve rotatably disposed in said air inlet, means controlling said air valve whereby its rotative position is a measure of the rate of air flow through said air inlet, a fuel bowl, a fuel passage receiving fuel from said fuel bowl and discharging fuel into said mixture conduit, a metering orifice disposed in said fuel passage, a metering rod associated with said metering orifice and controlling the area thereof to control the rate of fuel flow from said fuel bowl through said passage and said orifice to said mixture conduit, a pivot pin, a lever pivoted on said pin, said lever having a first lever arm connected to said metering rod and a second lever arm, a link connected to said air valve and to said second lever arm whereby the positions of said lever and said metering rod are controlled by the rotative position of said air valve and the rate of fuel flow through said passage to said mixture conduit is proportioned to the rate of air flow through said air inlet, said second lever arm having a slot fon'ned therein and receiving said link, and operating condition responsive means controlling the position of said link in said slot whereby the length of said second lever arm may be varied to adjust the proportion of fuel flow to air flow, said operating condition responsive means including a pivoted supplementary [ever having one lever arm connected to said link and another lever arm, an aneroid responsive to inlet air pressure and temperature and having one end thereof connected to said other lever arm and operative to pivot said supplementary lever to move said link in said slot away from said pivot pin upon a decrease in inlet air pressure or an increase in inlet air temperature, and a device responsive to pressure in said mixture conduit downstream of said throttle connected to the other end of said aneroid and operative to move said aneroid and thereby pivot said supplementary lever to move said link in said slot away from said pivot pin upon a decrease in such mixture conduit pressure below a selected level whereby the area available for fuel flow through said metering orifice may be decreased upon a decrease in inlet air pressure, an in crease in inlet air temperature, or a decrease in such mixture conduit pressure below such level.

5. A carburetor comprising a mixture conduit having an air inlet and a mixture outlet, a throttle disposed in said mixture outlet and controlling flow therethrough, an air valve rotatably disposed in said air inlet, means controlling said air valve whereby its rotative position is a measure of the rate of air flow through said air inlet, a fuel bowl, a fuel passage receiving fuel from said fuel bowl and discharging fuel into said mixture conduit, a metering orifice disposed in said fuel passage, a metering rod associated with said metering orifice and controlling the area thereof to control the rate of fuel flow from said fuel bowl through said passage and said orifice to said mixture conduit, a pivot pin, a lever pivoted on said pin, said lever having a first lever arm connected to said metering rod and a second lever arm, a link connected to said air valve and to said second lever arm whereby the positions of said lever and said metering rod are controlled by the rotative position of said air valve and the rate of fuel flow through said passage to said mixture conduit is proportioned to the rate of air flow through said air inlet, said second lever arm having a slot formed therein and receiving said link, operating condition responsive means controlling the position of said link in said slot whereby the length of said second lever arm may be varied to adjust the propor tion of fuel flow to air flow, said operating condition responsive means including a pivoted supplementary lever having one lever arm connected to said link and another lever arm, an aneroid responsive to inlet air pressure and temperature and having one end thereof connected to said other lever arm and operative to pivot said supplementary lever to move said link in said slot away from said pivot pin upon a decrease in inlet air pressure or an increase in inlet air temperature, and a device responsive to pressure in said mixture conduit downstream of said throttle connected to the other end of said aneroid and operative to move said aneroid and thereby pivot said supplementary lever to move said link in said slot away from said pivot pin upon a decrease in such mixture conduit pressure below a selected level, whereby the area available for fuel flow through said metering orifice may be decreased upon a decrease in inlet air pressure, an increase in inlet air temperature, or a decrease in such mixture conduit pressure below such level, a pivoted additional lever carrying said pivot pin, and temperature responsive means pivoting said additional lever whereby the proportion of fuel flow to air flow may be increased upon a decrease in temperature.

6. A carburetor comprising means defining a down draft mixture conduit, a fuel bowl disposed beside said mixture conduit, a cover disposed above said fuel bowl and having an upwardly extending rim disposed thereabout, a fuel passage extending from said fuel bowl to said mixture conduit, and a metering orifice disposed in said passage, a metering rod having one end disposed in said orifice and controlling the area thereof to control the rate of fuel flow from said fuel bowl through said passage and said orifice to said mixture conduit, an air valve disposed in said mixture conduit and rotatable between closed and open positions, means controlling said air valve whereby its rotative position is a measure of the rate of air flow through said mixture conduit, a first pivot pin disposed above said cover within said rim, a first lever disposed above said cover within said rim and pivoted on said pin and having a slot formed therein, a first link having one end connected to said air valve and having the other end received in said slot for raising said lever about said pin as said air valve is moved from its closed position, a hanger having one end connected to said lever and extending through said cover and having the other end connected to said metering rod for positioning said metering rod to control the rate of said fuel flow in accordance with the posi tion of said lever and thus in accordance with the rotative position of said air valve and thereby in accordance with the rate of said air flow, a second link disposed above said cover within said rim and having one end connected to said other end of said first link for varying its position in said slot to thereby vary the relative movement of said lever and said air valve and thus the proportions of said air flow and said fuel flow, a second pivot pin disposed above said cover within said rim, a second lever disposed above said cover within said rim and pivoted on said second pin and connected to the other end of said second link, a third link disposed above said cover within said rim and having one end connected to said lever, and operating condition responsive means connected to the other end of said third link for moving said third link to pivot said second lever to move said second link to vary the position of said other end of said first link in said slot to thereby vary the proportions of said air flow and said fuel flow in accordance with operating conditions.

7. A carburetor comprising means defining a downdraft mixture conduit, a fuel bowl disposed beside said mixture conduit, the bottom of said fuel bowl having a depression defining an upwardly opening well, a cover disposed above said fuel bowl, a straight fuel passage extending upwardly and transversely from a lower end opening axially from said well to an upper end opening laterally into said mixture conduit, and a metering orifice disposed in said passage near said upper end, a me tering rod disposed in said passage and having one end disposed in said orifice and controlling the area thereof to control the rate of fuel flow from said fuel bowl through said passage and said orifice to said mixture conduit, said metering rod having its other end extending into said well, a hanger having one end connected to said other end of said metering rod and extending through said cover, a lever pivotally disposed above said cover and connected to the other end of said hanger, an air valve rotatably disposed in said mixture conduit, means controlling said air valve whereby its rotative position is a measure of the rate of air flow through said mixture conduit, and a link connecting said air valve and said lever whereby said air valve and said metering rod are moved in unison to proportion the rate of fuel flow through said metering orifice to said mixture conduit to the rate of air flow through said mixture conduit.

8. A carburetor comprising a mixture conduit having an air inlet and a mixture outlet, a throttle disposed in said mixture outlet and controlling flow therethrough, an air valve rotatably disposed in said air inlet, means controlling said air valve whereby its rotative position is a measure of the rate of air flow through said air inlet, a fuel bowl, a fuel passage receiving fuel from said fuel bowl and discharging fuel into said mixture conduit, a metering orifice disposed in said fuel passage, a metering rod associated with said metering orifice and controlling the area thereof to control the rate of fuel flow from said fuel bowl through said passage and said orifice to said mixture conduit, a pivot pin, a lever pivoted on said pin, said lever having a first lever arm connected to said metering rod and a second lever arm, a link connected to said air valve and to said second lever arm whereby the positions of said lever and said metering rod are controlled by the rotative position of said air valve and the rate of fuel flow through said passage to said mixture conduit is proportioned to the rate of air flow through said air inlet, said second lever arm having a slot formed therein and receiving said link, and operating condition responsive means controlling the position of said link in said slot whereby the length of said second lever arm may be varied to adjust the proportion of fuel flow to air flow. 

1. A carburetor comprising a mixture conduit having an air inlet and a mixture outlet, a throttle disposed in said mixture outlet and controlling flow therethrough, an air valve rotatably disposed in said air inlet, means controlling said air valve whereby its rotative position is a measure of the rate of air flow through said air inlet, a fuel bowl, a fuel passage receiving fuel from said fuel bowl and discharging fuel into said mixture conduit, a metering orifice disposed in said fuel passage, a metering rod associated with said metering orifice and controlling the area thereof to control the rate of fuel flow from said fuel bowl through said passage and said orifice to said mixture conduit, a pivot pin, a lever pivotEd on said pin, said lever having a first lever arm connected to said metering rod and a second lever arm, a link connected to said air valve and to said second lever arm whereby the positions of said lever and said metering rod are controlled by the rotative position of said air valve and the rate of fuel flow through said passage to said mixture conduit is proportioned to the rate of air flow through said air inlet, said second lever arm having a slot formed therein and receiving said link, and operating condition responsive means controlling the position of said link in said slot whereby the length of said second lever arm may be varied to adjust the proportion of fuel flow to air flow, said operating condition responsive means including an aneroid responsive to inlet air pressure and operative to increase the length of said second lever arm upon a decrease in inlet air pressure whereby a proper proportion of fuel flow to air flow is maintained upon a decrease in inlet air pressure.
 2. A carburetor comprising a mixture conduit having an air inlet and a mixture outlet, a throttle disposed in said mixture outlet and controlling flow therethrough, an air valve rotatably disposed in said air inlet, means controlling said air valve whereby its rotative position is a measure of the rate of air flow through said air inlet, a fuel bowl, a fuel passage receiving fuel from said fuel bowl and discharging fuel into said mixture conduit, a metering orifice disposed in said fuel passage, a metering rod associated with said metering orifice and controlling the area thereof to control the rate of fuel flow from said fuel bowl through said passage and said orifice to said mixture conduit, a pivot pin, a lever pivoted on said pin, said lever having a first lever arm connected to said metering rod and a second lever arm, a link connected to said air valve and to said second lever arm whereby the positions of said lever and said metering rod are controlled by the rotative position of said air valve and the rate of fuel flow through said passage to said mixture conduit is proportioned to the rate of air flow through said air inlet, said second lever arm having a slot formed therein and receiving said link, and operating condition responsive means controlling the position of said link in said slot whereby the length of said second lever arm may be varied to adjust the proportion of fuel flow to air flow, said operating condition responsive means including a device responsive to inlet air temperature and operative to increase the length of said second lever arm upon an increase in inlet air temperature whereby a proper proportion of fuel flow to air flow is maintained upon an increase in inlet air temperature.
 3. A carburetor comprising a mixture conduit having an air inlet and a mixture outlet, a throttle disposed in said mixture outlet and controlling flow therethrough, an air valve rotatably disposed in said air inlet, means controlling said air valve whereby its rotative position is a measure of the rate of air flow through said air inlet, a fuel bowl, a fuel passage receiving fuel from said fuel bowl and discharging fuel into said mixture conduit, a metering orifice disposed in said fuel passage, a metering rod associated with said metering orifice and controlling the area thereof to control the rate of fuel flow from said fuel bowl through said passage and said orifice to said mixture conduit, a pivot pin, a lever pivoted on said pin, said lever having a first lever arm connected to said metering rod and a second lever arm, a link connected to said air valve and to said second lever arm whereby the positions of said lever and said metering rod are controlled by the rotative position of said air valve and the rate of fuel flow through said passage to said mixture conduit is proportioned to the rate of air flow through said air inlet, said second lever arm having a slot formed therein and receiving said link, and operating condition responsive means controlling the position of Said link in said slot whereby the length of said second lever arm may be varied to adjust the proportion of fuel flow to air flow, said operating condition responsive means including a device responsive to pressure in said mixture conduit downstream of said throttle and operative to decrease the length of said second lever arm upon an increase in such pressure above a selected level whereby the proportion of fuel flow to air flow is increased upon an increase in such pressure above such level.
 4. A carburetor comprising a mixture conduit having an air inlet and a mixture outlet, a throttle disposed in said mixture outlet and controlling flow therethrough, an air valve rotatably disposed in said air inlet, means controlling said air valve whereby its rotative position is a measure of the rate of air flow through said air inlet, a fuel bowl, a fuel passage receiving fuel from said fuel bowl and discharging fuel into said mixture conduit, a metering orifice disposed in said fuel passage, a metering rod associated with said metering orifice and controlling the area thereof to control the rate of fuel flow from said fuel bowl through said passage and said orifice to said mixture conduit, a pivot pin, a lever pivoted on said pin, said lever having a first lever arm connected to said metering rod and a second lever arm, a link connected to said air valve and to said second lever arm whereby the positions of said lever and said metering rod are controlled by the rotative position of said air valve and the rate of fuel flow through said passage to said mixture conduit is proportioned to the rate of air flow through said air inlet, said second lever arm having a slot formed therein and receiving said link, and operating condition responsive means controlling the position of said link in said slot whereby the length of said second lever arm may be varied to adjust the proportion of fuel flow to air flow, said operating condition responsive means including a pivoted supplementary lever having one lever arm connected to said link and another lever arm, an aneroid responsive to inlet air pressure and temperature and having one end thereof connected to said other lever arm and operative to pivot said supplementary lever to move said link in said slot away from said pivot pin upon a decrease in inlet air pressure or an increase in inlet air temperature, and a device responsive to pressure in said mixture conduit downstream of said throttle connected to the other end of said aneroid and operative to move said aneroid and thereby pivot said supplementary lever to move said link in said slot away from said pivot pin upon a decrease in such mixture conduit pressure below a selected level whereby the area available for fuel flow through said metering orifice may be decreased upon a decrease in inlet air pressure, an increase in inlet air temperature, or a decrease in such mixture conduit pressure below such level.
 5. A carburetor comprising a mixture conduit having an air inlet and a mixture outlet, a throttle disposed in said mixture outlet and controlling flow therethrough, an air valve rotatably disposed in said air inlet, means controlling said air valve whereby its rotative position is a measure of the rate of air flow through said air inlet, a fuel bowl, a fuel passage receiving fuel from said fuel bowl and discharging fuel into said mixture conduit, a metering orifice disposed in said fuel passage, a metering rod associated with said metering orifice and controlling the area thereof to control the rate of fuel flow from said fuel bowl through said passage and said orifice to said mixture conduit, a pivot pin, a lever pivoted on said pin, said lever having a first lever arm connected to said metering rod and a second lever arm, a link connected to said air valve and to said second lever arm whereby the positions of said lever and said metering rod are controlled by the rotative position of said air valve and the rate of fuel flow through said passage to said mixture conduit iS proportioned to the rate of air flow through said air inlet, said second lever arm having a slot formed therein and receiving said link, operating condition responsive means controlling the position of said link in said slot whereby the length of said second lever arm may be varied to adjust the proportion of fuel flow to air flow, said operating condition responsive means including a pivoted supplementary lever having one lever arm connected to said link and another lever arm, an aneroid responsive to inlet air pressure and temperature and having one end thereof connected to said other lever arm and operative to pivot said supplementary lever to move said link in said slot away from said pivot pin upon a decrease in inlet air pressure or an increase in inlet air temperature, and a device responsive to pressure in said mixture conduit downstream of said throttle connected to the other end of said aneroid and operative to move said aneroid and thereby pivot said supplementary lever to move said link in said slot away from said pivot pin upon a decrease in such mixture conduit pressure below a selected level, whereby the area available for fuel flow through said metering orifice may be decreased upon a decrease in inlet air pressure, an increase in inlet air temperature, or a decrease in such mixture conduit pressure below such level, a pivoted additional lever carrying said pivot pin, and temperature responsive means pivoting said additional lever whereby the proportion of fuel flow to air flow may be increased upon a decrease in temperature.
 6. A carburetor comprising means defining a downdraft mixture conduit, a fuel bowl disposed beside said mixture conduit, a cover disposed above said fuel bowl and having an upwardly extending rim disposed thereabout, a fuel passage extending from said fuel bowl to said mixture conduit, and a metering orifice disposed in said passage, a metering rod having one end disposed in said orifice and controlling the area thereof to control the rate of fuel flow from said fuel bowl through said passage and said orifice to said mixture conduit, an air valve disposed in said mixture conduit and rotatable between closed and open positions, means controlling said air valve whereby its rotative position is a measure of the rate of air flow through said mixture conduit, a first pivot pin disposed above said cover within said rim, a first lever disposed above said cover within said rim and pivoted on said pin and having a slot formed therein, a first link having one end connected to said air valve and having the other end received in said slot for raising said lever about said pin as said air valve is moved from its closed position, a hanger having one end connected to said lever and extending through said cover and having the other end connected to said metering rod for positioning said metering rod to control the rate of said fuel flow in accordance with the position of said lever and thus in accordance with the rotative position of said air valve and thereby in accordance with the rate of said air flow, a second link disposed above said cover within said rim and having one end connected to said other end of said first link for varying its position in said slot to thereby vary the relative movement of said lever and said air valve and thus the proportions of said air flow and said fuel flow, a second pivot pin disposed above said cover within said rim, a second lever disposed above said cover within said rim and pivoted on said second pin and connected to the other end of said second link, a third link disposed above said cover within said rim and having one end connected to said lever, and operating condition responsive means connected to the other end of said third link for moving said third link to pivot said second lever to move said second link to vary the position of said other end of said first link in said slot to thereby vary the proportions of said air flow and said fuel flow in accordance with operating conditions.
 7. A carburEtor comprising means defining a downdraft mixture conduit, a fuel bowl disposed beside said mixture conduit, the bottom of said fuel bowl having a depression defining an upwardly opening well, a cover disposed above said fuel bowl, a straight fuel passage extending upwardly and transversely from a lower end opening axially from said well to an upper end opening laterally into said mixture conduit, and a metering orifice disposed in said passage near said upper end, a metering rod disposed in said passage and having one end disposed in said orifice and controlling the area thereof to control the rate of fuel flow from said fuel bowl through said passage and said orifice to said mixture conduit, said metering rod having its other end extending into said well, a hanger having one end connected to said other end of said metering rod and extending through said cover, a lever pivotally disposed above said cover and connected to the other end of said hanger, an air valve rotatably disposed in said mixture conduit, means controlling said air valve whereby its rotative position is a measure of the rate of air flow through said mixture conduit, and a link connecting said air valve and said lever whereby said air valve and said metering rod are moved in unison to proportion the rate of fuel flow through said metering orifice to said mixture conduit to the rate of air flow through said mixture conduit.
 8. A carburetor comprising a mixture conduit having an air inlet and a mixture outlet, a throttle disposed in said mixture outlet and controlling flow therethrough, an air valve rotatably disposed in said air inlet, means controlling said air valve whereby its rotative position is a measure of the rate of air flow through said air inlet, a fuel bowl, a fuel passage receiving fuel from said fuel bowl and discharging fuel into said mixture conduit, a metering orifice disposed in said fuel passage, a metering rod associated with said metering orifice and controlling the area thereof to control the rate of fuel flow from said fuel bowl through said passage and said orifice to said mixture conduit, a pivot pin, a lever pivoted on said pin, said lever having a first lever arm connected to said metering rod and a second lever arm, a link connected to said air valve and to said second lever arm whereby the positions of said lever and said metering rod are controlled by the rotative position of said air valve and the rate of fuel flow through said passage to said mixture conduit is proportioned to the rate of air flow through said air inlet, said second lever arm having a slot formed therein and receiving said link, and operating condition responsive means controlling the position of said link in said slot whereby the length of said second lever arm may be varied to adjust the proportion of fuel flow to air flow. 